One of processes for dicing the substrate is known as a plasma dicing process which achieves plasma-etching the substrate with a mask thereon so as to divide it into a plurality of individual chips. Patent Document 1 (JP 2014-513868 A or U.S. Pat. No. 8,802,545 B2) discloses the method for plasma processing the substrate, in which the substrate is held on a conveying carrier that includes a holding sheet and a frame adhered on a periphery thereof and the substrate is set on a stage provided within a plasma processing apparatus, for ease of the handling of the substrate during delivery thereof.
Although the frame is designed to typically have a flat surface, the flatness thereof may be insufficient due to deviation and/or tolerance in manufacturing thereof and wear by repeated use in a production line. The insufficient flatness of the frame likely crimps the holding sheet adhered thereon.
The plasma treatment is carried out while the conveying carrier is set on and contacted on the stage by an electrostatic chucking mechanism called as an electrostatic chuck. The electrostatic chucking mechanism pulls or sticks the holding sheet onto the stage by means of the coulomb force or Johnson-Rahbek force between the Electrostatic Chuck electrode (referred to as ESC electrode) provided within the stage and the holding sheet, upon application of voltage with the ESC electrode. The crimps on the holding sheet may cause it pulled or stuck on the stage with a portion raised from the stage. This causes an insufficient contact between the stage and the sheet holding the substrate. The thinner substrate makes the contact therebetween further insufficient, because the lighter weight of the substrate can less effectively spread the crimps on the holding sheet.
The insufficient contact between the stage and the sheet holding the substrate distorts a plasma sheath generated at an interface between the substrate and the plasma atmosphere so that the substrate is unevenly etched, and therefore causing variation of the processed configuration and/or generation of unprocessed portions. Also, the insufficient contact may cause a temperature of the substrate raised at local regions and/or an abnormal discharge. The raised temperature and the abnormal discharge may damage the ESC electrode as well as the substrate and the holding sheet, which eventually deteriorates the production yield of the element chips obtained by the plasma processing method.